DDDR/2 - Glossary

This glossary contains terms and definitions that are, for the most part, used for OS/2 products. This is not a complete dictionary of computer terms.

Introduction

This glossary defines many of the terms used in this book. It includes terms and definitions from the IBM Dictionary of Computing, as well as terms specific to the Presentation Manager, but it is not a complete glossary for OS/2.

Other primary sources for these definitions are:

• The American National Standard Dictionary for Information Systems, ANSI X3.172-1990, copyrighted 1990 by the American National Standards Institute, 11 West 42nd Street, New York, New York 10036. These definitions are identified by the symbol (A) after the definition.
• The Information Technology Vocabulary, developed by Subcommittee 1, Joint Technical Committee 1, of the International Organization for Standardization and the International Electrotechnical Commission (ISO/IEC JTC1/SC1). Definitions of published parts of this vocabulary are identified by the symbol (I) after the definition; definitions taken from draft international standards, committee drafts, and working papers being developed by ISO/IEC JTC1/SC1 are identified by the symbol (T) after the definition, indicating that final agreement has not yet been reached among the participating National Bodies of SC1.

A

ABIOS

Advanced BIOS. See BIOS.

accumulator

1. A register in which one operand of an operation can be stored and subsequently replaced by the result of that operation. (T)
2. In the IBM 3800 Printing Subsystem Models 3 and 8, a feature that supplies a separate storage that can hold data in raster form. It can be used either for composing a sheet of data that combines a large amount of variable and constant data, or for storing an electronic overlay in raster form that will be merged with variable data as the sheet is printed.

access permission

All access rights a user has regarding an object. (I)

adapter

A piece of hardware that modifies the system unit to allow it to operate in a particular way, often by connecting the system unit to an external device such as a video monitor.

adapter device driver

A device driver that provides hardware-dependent services for an OEM adapter.

address space

1. The range of addresses available to a program. (A)
2. The area of virtual storage available for a particular job.

all points addressable (APA)

In computer graphics, pertaining to the ability to address and display or not display each picture element (pel) on a display surface.

anchor block

An area of the internal resources of OS/2 Presentation Manager which is allocated to a process or thread that calls WinInitialize.

anchor point

The position or choice from which selection or deselection is extended.

APA

All points addressable.

API

Application programming interface.

application programming interface (API)

A functional interface supplied by the operating system, or by a separately-orderable licensed program, that allows an application program written in a high-level language to use specific data or functions of the operating system or the licensed program.

archive flag

In the OS/2 operating system, a flag of files and directories that the operating system uses to determine which files are new or modified. Files with this flag are included when a backup copy is made or when all the files are restored on a hard disk. See flag.

area

In computer graphics, a filled shape such as a solid rectangle.

ASCIIZ

A string of ASCII characters that is terminated with a byte containing the value 0.

aspect ratio

1. The ratio of the height of a rectangle to its width. A rectangle of width 10 inches and height 5 inches has an aspect ratio of 10/5 or 2.
2. On a display screen, the ratio of the maximum length of a display line to the maximum length of a display column.

asynchronous (ASYNC)

1. Pertaining to two or more processes that do not depend upon the occurrence of specific events such as common timing signals. (T)
2. Without regular time relationship; unexpected or unpredictable with respect to the execution of program instructions.

atom

A constant that represents a string. Once a string has been defined as an atom, the atom can be used in place of the string to save space. Strings are associated with their respective atoms in an atom table. See integer atom.

atom table

A table used to associate atoms with the strings that they represent. This table contains the mechanism by which the presence of a string can be verified.

AVIO

Advanced Video Input/Output

B

background color

The color assigned to a background image.

background mix

An attribute that determines how the background of a graphic primitive is combined with the existing color of the graphics presentation space.

base device driver

An OS/2 device driver that performs I/O during the OS/2 kernel boot sequence to provide IPL support. Base device drivers are loaded by way of the CONFIG.SYS BASEDEV keyword, rather than the DEVICE keyword. See BASEDEV keyword, adapter device driver, and device manager.

BASEDEV keyword

New CONFIG.SYS keyword; loads a base device driver into the operating system.

Basic Input/Output System (BIOS)

Code that controls basic hardware operations, such as interactions with diskette drives, hard disk drives, and the keyboard.

Bezier curve

A mathematical technique of specifying a smooth, continuous line or surface, requiring a starting point and an ending point, with several intermediate points that influence or control the path of the linking curve.

BIOS

Basic Input/Output System.

bit-block transfer (bitblt)

Transfer of a rectangular array of bit-map data.

bitblt

Bit-block transfer.

bit map

A representation of an image by an array of bits.

block

1. In programming languages, a compound statement that coincides with the scope of at least one of the declarations contained within it. A block may also specify storage allocation or segment programs for other purposes. (I)
2. A string of data elements recorded or transmitted as a unit. The elements may be characters, words or physical records. (T)
3. A collection of contiguous records recorded as a unit. Blocks are separated by interblock gaps and each block may contain one or more records. (A)

Bit block transfer (bitblt)

The process of transferring one or more blocks of data.

border

A visual indicator of a window's boundaries.

BPB

BIOS Parameter Block.

breakpoint

1. A point in a computer program where execution may be halted. A breakpoint is usually at the beginning of an instruction where halts, caused by external intervention, are convenient for resuming execution. (T)
2. An instruction in a program for halting execution. Breakpoints are usually established at positions in a program where halts, caused by external intervention, are convenient for restarting. (T)
3. A place in a program, specified by a command or a condition, where the system halts execution and gives control to the workstation user or to a specified program.

Bus Master adapter

An adapter capable of performing Reads and Writes to physical storage by communicating directly with the storage subsystem (memory) rather than depending on a host DMA channel or host CPU. Synonymous with first-party DMA adapter.

C

cached micro presentation space

A presentation space from a Presentation Manager owned store of micro presentation spaces. It can be used for drawing to a window only, and must be returned to the store when the task is complete.

CDB

Command Descriptor Block.

cell

See character cell.

character box

1. An imaginary parallelogram on a display surface that contains all parts of one graphic character. Synonymous with bounding box. (T)
2. The maximum area in which a symbol and all associated elements, such as a cursor, an underline, or space surrounding the symbol to separate it from other symbols, can be printed or displayed. Synonymous with character cell.
3. The imaginary parallelogram whose boundaries govern the size, orientation, and spacing of individual characters to be displayed on a graphics display device.

character cell

1. An addressable location on a display surface or printing medium.
2. The physical width and height in pels of a font. See also bounding box.
3. The imaginary box whose boundaries govern the size, orientation, and spacing of individual characters to be displayed on a workstation.

character mode

A mode that, in conjunction with the font type, determines the extent to which graphics characters are affected by the character box, shear, and angle attributes.

clipping

In computer graphics, removing those parts of display elements that lie outside of given boundary.

clip limits

The area of the paper that can be reached by a printer or plotter.

clipping path

A clipping boundary in world-coordinate space.

code page

An assignment of graphic characters and control function meanings to all code points; for example, assignment of characters and meanings to 256 code points for an 8-bit code, assignment of characters and meanings to 128 code points for a 7-bit code.

code point

A 1-byte code representing one of 256 potential characters.

code segment

An executable section of programming code within a load module.

color conversion

Changing one color format to another. Required, for example, when the source color format is different from the destination color format. When going from the monochrome color format to the color format, 1 (one) bits are converted to the image foreground color, and 0 (zero) bits are converted to the image background color.

When going from color to monochrome, all pels that match the passed background color are converted to the image background color of the destination.

All other pels are converted to the image foreground color of the destination. The color conversion takes place prior to any mix mode.

color dithering - See dithering.

command code

In this specification, refers to a group of related commands that an adapter device driver can receive.

All command codes have a prefix of "IOCC_". For example, common I/O requests (such as Read, Write, etc.) are grouped under the command code IOCC_EXECUTE_IO.

command data block

A data structure defined by the Small Computer System Interface standard to send commands to devices that conform to SCSI standards.

command descriptor block (CDB)

The structure used to communicate commands from a source to a destination.

command modifier

In this specification, a specific operation that an adapter device driver is to perform.

All command modifiers have a prefix of "IOCM_". For example, an adapter device driver might receive an IOCC_EXECUTE_IO command with a command modifier of IOCM_READ.

compatibility kernel

The portion of the OS/2 kernel that exists to support DOS INT 20, 21, 25, 26, and 27 functions. It acts as an interface to common kernel functionality such as the file system.

CON

Character-device name reserved for the console keyboard and screen.

conditional compilation

Processing by the preprocessor of certain specified code in the file, depending on the evaluation of a specified condition.

context hook

Similar to a "force flag" in earlier versions of OS/2. These are events, signaled by a virtual device driver, that are processed at task time. Forcing an IRET, and simulating an NMI, can fall into this category.

control program

A computer program designed to schedule and to supervise the execution of programs of a computer system.

controller sector buffer

One or more buffers, managed by a hardware adapter, to improve I/O transfer rates by helping to match a device and software timing requirements.

T

text window

See VIO window.

thread

The smallest unit of operation to be performed within a process.

thunk

term used to describe the process of address conversion, stack, and structure realignment that is necessary when passing control between 16-bit and 32-bit modules.

thunk layer

An interface that converts 32-bit parameters to 16-bit parameters, and maps linear addresses to segmented addresses.

time slice

1. The period of processing time allocated for running a program.
2. An interval of time on the processing unit allocated for use in performing a task. After the interval has expired, processing unit time is allocated to another task, so a task cannot monopolize processing unit time beyond a fixed limit.

tuple

In a relational database, a part of a relation that uniquely describes an entity and its attribute.

U

unnamed pipe

A circular buffer created in memory; used by related processes to communicate with one another. Contrast with named pipe.

V

VBIOS

Virtual BIOS device driver

VCMOS

Virtual CMOS device driver

VDD

Virtual device driver

VDH

Virtual video Device Handler

VDM

Virtual DOS Machine; use DOS session.

VDMA

Virtual Direct Memory Access device driver

VDSK

Virtual hard DiSK device driver

video graphics adapter (VGA)

A computer adapter that provides high-resolution graphics and a total of 256 colors.

VIO

Virtual Input/Output

VIRR

Virtual Interrupt Request Register

Virtual Device Driver (VDD)

In the OS/2 operating system, a type of device driver used by DOS programs running in a DOS session to access devices, such as the screen or mouse, which must be shared with other processes in the system. The virtual device driver maps DOS device commands to the normal (physical) device driver under OS/2 2.0 and later versions of the operating system.

virtual DevHlp (VDH)

Kernel (linear memory, paging, hardware interrupt, event control, port control) services provided to virtual device drivers.

virtual I/O (VIO)

A facility that pages data into and out of external page storage.

virtual memory

Synonym for virtual storage.

Virtual Programmable Interrupt Controller

Virtualizes the 8259 Programmable Interrupt Controller (PIC). A special virtual device driver, in that it provides services to other virtual device drivers.

virtual storage

Addressable space that is apparent to the user as the processor storage space, from which the instructions and the data are mapped into the processor storage locations. Synonymous with virtual memory.

visible region

A window's presentation space clipped to the boundary of the window and the boundaries of any overlying window.

VPIC

Virtual Programmable Interrupt Controller device driver.

VRAM

Video Random-Access Memory.

VTIMER

Virtual TIMER device driver.

V86 mode

Virtual 8086 mode of the 80386 CPU.

W

window coordinates

A set of coordinates by which a window position or size is defined; measured in device units, or pels.